The present invention utilizes an electric current which is placed across electrodes at both ends of a sealed bulb, which has a fluorescent material on its inner diameter and is filled with various gases or vapors, which are subjected to electron bombardment emitted from the electrodes, causing collisions with the outer electrons in orbit around the nucleous of the atoms of gas causing disruption of the atom's electron orbit, wherein ultraviolet photon energy is created, which in turn strikes the fluorescent coating on the inner diameter of the bulb causing it to emit visible light. It happens that an electron disruption of a low pressure mercury vapor produces an abundance of one particular wavelength in this short-wave ultraviolet region and phosphors are selected and blended to respond efficiently at that wavelength as to produce different colors of visible light.
Fluorescent compounds can be conveniently divided into two classes: those excited by higher frequency and thos excited by lower frequency ultraviolet radiation. This radiation occurs when a gas or vapor is electrically excited and this emission may take place in a series of steps, each step from a highly excited state to some lower state of excitation being marked by radiation at a wavelength peculiar to that step. The many millions of excited atoms enclosed in a discharge tube thus returns to normal by one or more stages; some in two, others in three, and so on: but with any given conditions of pressure, current density, etc., in a particular gas or vapor, the relative numbers of atoms returning to their normal state by any of the alternative paths is fixed at a definite proportion of the whole. Each of the radiations characteristic of the gas or vapor are therefore emitted, but some are stronger than others; and by careful control of the current density and pressure it is possible to some extent to alter the relative strengths of these radiations.